A method for study of the degradation of radiolabelled synthetic calcium pyrophosphate dihydrate (CPPD) crystals by cultured rabbit, dog and human synovial cells has been developed. The influence of induced synovial cell hemosiderosis on the rate of degradation, and the nature and location of degradative enzymes will be studied. The activities of 5' nucleotidase and inorganic pyrophosphatases will be studied in intact rabbit chondrocytes just after enzymatic release from cartilage and after growth in monolayer culture, and in homogenates prepared from these cells. The interaction of CPPD, hydroxyapatite and other crystals with cultured synovial cells from several species is under study with particular reference to the release of collagenase, neutral protease and prostaglandins in follow-up of the recently described "Milwaukee Shoulder" syndrome where these substances were associated with glenohumeral osteoarthritis and loss of the rotator cuff. The fate of the monolayer of IgG adsorbed to monosodium urate crystals is being examined after phagocytosis by polymorphonuclear leukocytes. Biochemical and microscopic approaches both show rapid removal of protein from the crystal surface. Study of the interaction of other proteins adsorbed to microcrystals is underway.